Thorium-carbon alloys



United States Patent 6) 2,872,397. THORIUM-CARBON'ALLOYS Harley A.Wilhelm and Robert E Rundle, Ames, Iowa,

This invention relatesto; alloys .Qf;thriurn and carbon;

and-more. particularly tothoriumycarbon alloyshaving a low carboncontent.

An object of this-inventionq-is to provide, a thoriumcarbonl alloyhaving a selected low. carbon content and;

preferably a thorium-carbonalloy containing theper,- centage of carbonwithin those certain; limits-WhichgWilL impart to the cast alloyproperties; superior to those.

found inpure thorium metal.

A further object of this invention; is. to provide a new composition ofmatter,- .namely,. thorium, monocarbide ('IhC).

A further object' of this, invention is, to. provide a thorium-carbonalloy wherein. the. carbon presentas a solid solution in thorium metal.is present in the-form of the compound, thorium monocarbide.

Other objects and advantages of this invention will.

be readily apparent from thefollowingdescription of the preferredembodiments of this invention.

The compositions of matter 'comprisingthe subject matter of thisinvention possess properties which-. make them useful in processesinvolving; nuclear bombardment under conditions peculiar to thosefoundin chain-reacting piles. The particular carbon content found in thesecompositions of matter imparts, tothemthe.- properties of increasedhardness and resistance to corrosion from contact with hot, aqueous:solutions.

In accordance withpthist invention, carbon is incorporated into thoriummetal to produce the compound, thorium monocarbide, and mixturesconsisting of thorium metal and thorium. monocarbide. Thewmonocarbideand mixtures of thorium metal with thorium monocarbide I possess greaterhardnessgand resistance:tocorrosiomt thorium metal alone.

The thorium alloyvcomprisinggthe subject matter'of this inventioncontains; a carbon: content between;v 0.1; and4.9%. by weight: carbon.Generally, theihardness, values increase directly; with; theincreaseingcarbon content, and those thorium-carbon alloys containing between0.1 and 2% by weight carbon are preferred. Alloys containing 0.1 to 0.5%carbon are especially preferred.

The alloys or compositions of matter comprising this invention areprepared by heating thorium metal with carbon at a temperature above themelting point of thorium, for example, at 1800 to 2000 C. in an inertrefractory crucible. The reaction may be carried out in a vacuum or inthe presence of an inert gas, such as argon and helium, to preventthorium oxide formation.

When using a graphite vessel in the casting of thorium, the carbon of agraphite vessel reacts with thorium in suificient quantity to introduceless than 0.1% carbon which occurs as carbide in the metal both as grainboundary and intergranular inclusions. However, in a method of preparingthe alloys of this invention pure thorium is heated for a prolongedperiod of time above its melting point in a graphite crucible wherebythorium and graphite react to produce the alloys. The carbon 2 contentof the alloy is. determined by the :.time ofheat ing thorium in thecruciblefor a: particular temperature; The amount of carbon therebyintroduced may;be.varied between 0.1.and4;9% by weight.Thorium-carbontale loys of this invention having low carboncontents,such as 0.1 to 2%, maybe prepared byfusingthoriumwith an appropriateamount ofcarbon in a, crucibleof, a refractory. oxide, such as .thoria,usingan, atomic hydro.- gen arc.

After the fused alloy is obtainedbyany. of'thefore going. methods, itmaybe water-quenchedor furnacecooledin an inert atmosphere from thereaction temperature.

We have discovered that castalloys ofjthorium, C0117 taining between0.1' and 0.5 by weig'htcarbon are moretained in a 400-cc. beaker whichwas then covered with a Petri dish and heated in an autoclave bysteam.atl-178= C. under apressure of125 lbs per square inch. At cer.-*min intervals, the specimens were removed from. the water, dried 'withacetone, weighed; and placed'back'irr the waterin, the autoclave for:continued 1 treatment: Table I summarizes thevextent of corrosionobserved in a thorium alloy containing 0.3% carbon and in pure thoriummetal.

' TABLET" Total Wt. Change mgJcmfi/hr.

Time in Test, hrs. v

Purellh The1data indicate that. the.loss in::weight; dueatoucorrosionof: purethorium is much, greaterythan'. the- IOSSTJOf V the thorium:alloy;

When alloys: of;- the.- present. inventionr ar,ewater: quenched. from"elevated temperatures; 6; g 1 C., the ;hardness.: of the alley: isdetermined: byvthe: carbon content. By increasing the carbon content thehardness of the alloy increases. However, it was found that bysubsequent annealing of these water-quenched alloys at elevatedtemperatures, such as 700, 800, 900, and 1000 C., for six hours andfollowed by furnace-cooling, the alloys containing greater than 0.5%carbon lost substantial amounts of their hardness. In all cases thesealloys still had hardness values greater than alloys containing' lessthan 0.5% carbon. The latter alloys exhibited substantially no change inhardness when subjected to this annealing treatment and they areaccordingly alloys of relatively permanent hardness.

Apparently, carbon is soluble in thorium metal as a solid solution ofthorium monocarbide. At 900 C., carbon is soluble in thorium to theextent of less than 0.12%. At 1000' C. the solubility limit for carbonin thorium is between 0.32 and 0.44% carbon, while at 1100 C., between0.44 and 0.74% by weight carbon is invention.

soluble in thorium metal. These valuues expressed in percent by weightof thorium monocarbide would be:

At 900 C. 2.44% ThC At 1000 C. from 6.5 to 829% ThC At 1100 C. from 8.9to 15% ThC carbide phase is identified by a face-centered cubic NaCltypestructure having a lattice parameter a =5.29 A. Determinations oflattice parameter were determined by obtaining aback reflection patternfrom ,a polished surface of the alloy sample. The lattice parameter forpure thorium metal is 5074:0002 A. at 20 C., which value increasesdirectly with an increase in the percent carbon present in the sampleandthe temperature at which the alloy is heated and subsequentlywater-quenched. Such data indicate that the presence of carbon expandsthe crystal lattice structure of metal and furnishes additional evidencefor the solid solubility of carbon in thorium.

Example I A sample of thorium metal was fused in an atomic hydrogen arcin the presence of carbon. The resultant product was ground and polishedand an average hardness of 53 on the Rockwell A scale was measured. X-ray data revealed the presence of three phases, namely, thorium metal,thorium dioxide, and thorium monocarbide. Chemical analysis of thisproduct show 0.34% carbon and 90% thorium. Photomicrogr'aphs showed thepresence of a dendritic monocarbide pattern.

Example ,11 j

A sample of thorium metal was fused in a graphite crucible and theresultant product was found to contain 1.2% carbon and 98.5% totalthorium (84.8% free thorium as determined by hydrogen evolution). TheX-ray diffraction pattern showed a lattice parameter for thorium a=5.094 A. and the thorium monocarbide lattice parameter 5.28 A., themonocarbide phase being a face-centered NaCl-type structure. The averagehardness was 62.1 on the Rockwell A scale which was equivalent toapproximately 100 on the Rockwell B scale. Examination of themicrostructure showed carbide in the grain boundaries and somedistribution of carbide throughout the crystal planes- Example III Athorium-zinc metal biscuit was heated in an induction furnace to atemperature of 1850 C. under high vacuum in a graphite crucible in orderto distill off the zinc impurity. When the vapor pressure had dropped toa low value, purified argon was introduced to prevent surface oxidationof the metal while cooling it.

pended claims.

The resultant metal contained 99% free thorium, 99.7% total thoriumand0.09% carbon.

A sample of this thorium metal, weighing 196.5 g., was heated in aberyllium oxide crucible with 0.492 g. of carbon to a temperature of 1850 C. for fifteen minutes and subsequently water-quenched from thistemperature. The average hardness value of the resultant thorium-carbonalloy was 93.9 on the Rockwell B scale. Chemical analysis showed 0.36%carbon. The X-ray diffraction pattern for the starting material showed alattice parameter a =5.0835:0.0004 A., while the lattice parameter forthe thorium-carbon product alloy was a =5.0887i0.0005 A.

Example IV The pure thorium metal used in'this experiment was preparedby thevacuum distillation of zinc from a zincthorium alloy as in ExampleIII.

One hundred sixty-eight grams of the dezinced thorium metal containing0.04% carbon was heated with 0.88 g. of carbon in a graphite cruciblelined with beryllia to a temperatureof 2000 C. The temperature waslowered by passing argon into the system and at 1850 C. the carboncrucible containing the sample was quenched in water. Average hardnessvalues on the Rockwell B scale measured 92.4 and the product contained0.59% by weight carbon. The lattice parameter of the starting materialwhich contained 0.04% carbon is equal to a =5.0794i0.0006 A., while theproduct lattice parameter was a =5.094i-0.0006 A.

The foregoing description presents the preferred embodiments of thisinvention 'in which are disclosed new and useful compositions of matter.Many alterations and changes, which will be apparent to those skilled inthe art, may be made therein without departing from the spirit and scopeof this invention as set forth in the ap- What is claimed is:

' 1. A thorium-carbon alloy consisting essentially of 0.1 to 0.5 byweight carbon and thorium.

2. A binary thorium-carbon alloy consisting of thorium and about 0.3% byweight carbon.

References Cited in the file of this patent FOREIGN PATENTS GreatBritain JainS, 1942 OTHER REFERENCES Troost: Comptes- Rendus, vol. 116,pp. 1229-1230- Moissan et al.: Annales de Chimie et du Physlque,

' Series 7, vol. '12, p. 432 (1897).

Mellor: Inorganic and Theoretical Chemistry, vol. 7, p. 210 (1927),publ. by Longmans, Green & Co., London.

1. A THORIUM-CARBON ALLOY CONSISTING ESSENTIALLY OF 0.1 TO 0.5% BYWEIGHT CARBON AND THORIUM.